Method for fabricating solid tire having polyurethane foam core

Abstract

A solid tire having a polyurethane foam core is fabricated by first mounting the tire on a two piece jig which simulates the wheel hub on which the tire is to be mounted. This jig is centered on the tire and tightened so that the inside surfaces of the two halves of the jig abut tightly against the tire body. A fill hole for filling the tire with foam is provided on one of the jig halves. A plurality of small holes are formed in the tire in a circle which runs along the high point of the outer surface of the tire, these vent holes being formed on the same side of the tire as the fill hole. The tire is then filled with a mixture of polyol and isocyanate through the fill hole to form a microcellular flexible polyurethane core within the tire. The core material is fed into the tire until the tire is filled a predetermined amount which with the expansion resulting from the chemical reaction, completely fills the tire as evidenced by material existing from the fill hole, at which time the fill hole is plugged. The jig is removed from the tire while the core material is still expanding to assure that such material is permitted to expand outwardly against the inner wall of the tire in tight abutment thereagainst and towards the center to assure a tight fit with the wheel hub on which it is subsequently installed.

I claim: 
     
       1. A method for fabricating a solid tire having a tire casing filled with a microcellular polyurethane foam forming a core comprising the steps of: installing a jig on the tire casing, said jig simulating the wheel hub with which the tire is to be used, said jig having two similar halves which are placed on opposite sides of the casing flush against each other and against the opposite outer surfaces of said casing, said jig being centered on the casing, the halves thereof being clamped flush against each other and in tight abutment against the opposite outer surfaces of the casing, said jig having a fill hole in one of the halves thereof which provides fluid communications between the interior of the casing and the exterior of the jig,   forming a plurality of vent holes in a circle along the high point on the outer casing wall against which said one of the halves of said jib abuts,   supporting the tire in a substantially horizontal position with the vent holes facing upwardly,   filling said casing through said fill hole with an amount of a liquid flexible microcellular polyurethane foam forming mixture composed of polyol and isocyanate such that said polyurethane foam, expanding in response to the chemical reaction of the mixture of said polyol and isocyanate, will completely fill said casing,   plugging said fill hole to contain the polyurethane foam within the casing, and   removing said jig from said casing a predetermined time period after the casing has been filled, while the polyurethane foam is still expanding, such that the polyurethane foam expands both towards the center of the casing and outwardly tightly against the casing so that it any remaining air is vented out through the vent holes to avoid the formation of air pockets in the casing.   
     
     
       2. The method of claim 1 wherein the mixture is a 50%--50% one. 
     
     
       3. The method of claim 1 wherein the mixture is 60% isocyanate and 40% polyol. 
     
     
       4. The method of claim 1 wherein the mixture is between 60%-50% isocyanate and 40%-50% polyol. 
     
     
       5. The method of claim 1 wherein while the casing is being filled with said mixture it is supported in a substantially horizontal position on the other of the halves of the jig. 
     
     
       6. The method of claim 1 wherein the vent holes include a first group of said vent holes which are equally spaced around the circle and a second group of said vent holes located on the side of said casing diametrically opposite to that on which the fill hole is located which are spaced half way between the holes of said first group. 
     
     
       7. The method of claim 1 wherein said tire casing is an 8×2 size and there are 8-9 vent holes. 
     
     
       8. The method of claim 1 wherein said tire casing is a 280/250-4 size and there are 10-11 vent holes. 
     
     
       9. The method of claim 1 wherein the jig is removed from the casing in 5-9 minutes after the casing is filled. 
     
     
       10. The method of claim 1 wherein the vent holes are 1/16" to 7/64" in diameter. 
     
     
       11. The method of claim 1 wherein the vent holes are large enought to permit air to escape and small enough to avoid the foam running out the holes as the foam expands. 
     
     
       12. The method of claim 8 wherein the casing is filled with the polyurethane forming mixture for approximately 4.7 seconds at a rate of 100 grams/sec. and the jig is removed from the casing approximately eight minutes after the tire has been filled. 
     
     
       13. The method of claim 7 wherein the casing is filled with the polyurethane forming mixture for approximately 2.7 seconds at a rate of 100 grams/sec. and the jig is removed from the casing approximately six minutes after the tire has been filled.